Expand.
We expand the parentheses using the distributive property : $ A(B+C+D)= A\cdot B+ A\cdot C+ A\cdot D$ We can also think about the problem using an area model: $7z^2$ $3z$ $-2$ $6z^2$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{6z^2}(7z^2+3z-2) \\\\ &={6z^2}(7z^2)+{6z^2}(3z)+{6z^2}(-2) \\\\ &=42z^4+18z^3-12z^2 \end{aligned}$ Here's how the solution looks in terms of the area model: $42z^4$ $18z^3$ $-12z^2$ $7z^2$ $3z$ $-2$ $6z^2$ In conclusion, $6z^2(7z^2+3z-2)=42z^4+18z^3-12z^2$